High intensity projection lamp



March 18, 1958 H. c. M. LONGACREY HIGH INTENSITY PROJECTION LAMP Filed March 21; 1955 INVENTOR HENRY C. M. LONG/1 CRE ATTORNEY i atent inert raorncrroN LAMP Henry C. M. Longacre, Glen Oaks, N. Y., assignor to Sylvania Electric Products, Inc a corporation of Massachusetts Application March 21, 1955, Serial No. 495,528

4 Claims. (Cl. 313-341) My invention relates to light producing devices.

In many phases of the lighting industry, and particularly in those portions of the industry which are concerned with the production of light sources for motion picture projectors, search lights and the like, it is necessary to provide a quasi-point source of high intensity light in Which the visible light spectra approximates that of the sun. conventionally, a carbon or zirconium arc is used forthis purpose. The apparatus required for the production of such an arc is complex and expensive; it must be supplied with power by special generators; it must be operated by highly skilled technicians.

I have devised a new type of lamp for use in applications of the above type which does not use an arc. This lamp can be supplied with power directly from a power line and no special generators or similar equipment is required. Moreover, this lamp can be operated automatically and no attendants or operators need be used.

Accordingly, it is an object of the invention to eliminate the use of carbon or zirconium arcs in the production of high intensity light.

Another object is to provide a new high intensity light source which does not use an arc.

Still another object is to provide a new high intensity lamp which operates on conventional single phase or multiphase alternating current.

Yet another object is to provide a new high intensity lamp in which an electrically heated refractory element is used as a light source.

A further object is to use incandescent refractory elements as high temperature sources of high intensity light.

Still a further object is to replace carbon or zirconium arcs with a light source formed from a refractory element electrically heated to temperatures on the order of thou sands of degrees Kelvin.

Yet a further object is to provide a new refractory element light source which is electrically heated to very high temperatures, the electrical energy being supplied from a conventional single phase or multiphase source of alternating current.

These and other objects of the invention will either be explained or will become apparent to those skilled in the art when this specification is studied in conjunction wiLh the accompanying drawings wherein:

Fig. 1 is a top view of a preferred embodiment of a refractory element light source in accordance with my invention;

Fig. 2 is a side view of this element; and

Fig. 3 is a cross sectional side view of a lamp assembly incorporating the element shown in Figs. 1 and 2.

In my invention, a refractory element having a thin disc-like center portion and two or more equidistantly spaced legs attached thereto is used as a light source. Current is supplied through the legs to the center portion to raise the temperature of the disc to such a value (ranging upward to about 4500 K.) that the disc becomes a light source. At these operating temperatures, the spectra of the emitted light approximates that of a carbon or zirconium arc.

Two legs are required for a single phase current source; three legs are required for a three phase current source; for other types of sources such as a six phase system the number of legs must be increased accordingly.

The legs must be shaped so that their cross sectional area increases with increasing distance from the center. This type of construction is necessary both to increase the ratio of disc to leg resistance, thereby concentrating the power consumption in the region of the disc, and to control the temperature gradient between the disc and legs in such a manner that the variation is gradual, thus preventing strains, crack formation and other undesirable surface and structural changes.

The element can be formed from one or more conventional high purity refractory materials such as tungsten, the carbides of tantalum, zirconium and hafnium and the like. These materials tend to oxidize rapidly and fail in oxygen-containing atmosphere. Consequently, the element is operated in an oxygen free atmosphere such as argon or other inert gas or a Vacuum.

The element can be mounted within a glass, quartz or vycor envelope and operated in an oxygen free atmosphere.

Electric power can be supplied from a conventional 60 cycle alternating current source; however, higher frequencies can be used if desired.

The element and the surrounding envelope containing built-in reflectors and an aperture mask can be assembled within a mounting support to form an integral lamp as described in more detail below.

Referring now to the drawing, Figs. 1 and 2 show a re fractory element identified generally at 1 and provided with a thin disc-like center portion 2 and a plurality of legs 3 extending outward from the center portion. The element illustrated is adapted for three phase current operation so that three equidistantly spaced legs are required. The number of legs required depends upon the number of phases used. For example, single phase operation would necessitate the use of two equidistantly spaced legs. it will be apparent that the cross sectional area of each leg increases with increasing distance from the center portion so that the electrical resistance of the center portion is much higher than that of the legs and the power consumption is concentrated in the center portion of the element. Moreover, this construction permits control of the temperature gradient in the manner previously described.

Fig. 3 is a cross section of a lamp assembly adapted for single phase operation. Two tungsten or other high temperature resistant conducting leads 10 extend through corresponding openings in an insulating support member 11, a single phase refractor element 12, and an insulated mask 13. The ends of leads adjacent the mask are swaged and are separated from the mask by insulating spacers 22. Element 12 and support member 11 are separated from each other by tungsten, nickel or molybdenum sleeves 14 and 15 which fit tightly around corresponding portions of leads 10. Sleeves 14 and 15 are connected to each other by tungsten or molybdenum springs. Sleeves 14 are free to move as thermal expansion takes place. Sleeves 15 are aflixed, for example, by spot welding, to the tungsten leads.

Mask 13 has an inner light reflecting surface 16 and a light aperture 17 mounted directly over the disc like portion 18 of element 12. Secured to the support member 11 and mounted below the disc portion 18 is a triple light reflector 19. The purpose of the reflectors and mask reflecting surface is to reflect as much radiant energy as possible back into the hot zone surrounding the disc. The aperture 17 is placed in front of the disc to concentrate the light into a small area and to insure that only the light from the discis transmitted. The disc'ls' at s1ibdisc like center portion and 'a plurality of equidistantly stantially uniform temperature and the lighternitted therefrom has a uniform spectra characteristic. Light from various'portions of the legs has a variable spectra characteri'stic and. would deleteriously affect; the; quality -of'.

light produced by the lamp.

The entire assembly is m ounted WithinIa :gas t'filled or evacuatedvenvelope 20 as :previously indicated.

Because of the highoperatingtemperatures =used, material Will be evaporated from the surface of elementf12 and will tend to deposit on the inner surfaceiofr the'envelope. In some cases, such deposition'can result in irn paired light transmission properties of the envelope.

However, if the'periphery' of mask, ,13'is provided with holes 21, and a 'gasfilledenvelopeis used, conventional currents set up within-the hottg'as,will causefthe gas to'circulate through the holes 21 and reduce thechimneyin-g of the gas. (with entrained particles of evaporated material') through the aperture and thus minimize the materialde' -1. An integral solid element formed from refractory material, said element being provided with a single thin t spaced legs extending from said portion, the cross sec,-v

tional area of each leg increasing with increasing distance from the center portion, the fiat surface of said central portion being substantially coplanar with the top surface of each of said legs.

2. An integral solid light source formed from refractory material, said source being provided with a single disc like center portionand a plurality of equidistantly spaced legs extending from said center portion, the elec- References Cited the file of this patent; UNITED STA I ES PATENTS 242;984' Reynier. June' 14, 1881 2 44,29 1 Perkins "July 12, 1881.

280,341 Bernstein July, 3,, 1883;-

, DoWsett Jan. '18, 1 927 

